1. Field of the Invention
The present invention relates to the field of timing devices. Specifically, the present invention is directed to a device for displaying the time on basis of a clock. The basic pulse generator for the clock is a low accuracy oscillator that is continuously functioning and supplies pulses. The device is also equipped with a micro-controller having a high accuracy clock that is switched off when the device is switched off.
2. Description of the Related Art
A low accuracy oscillator is known from the U.S. Pat. No. 3,911,373. According to this reference, an oscillation control circuit comprises an astable multivibrator and a display means such as a light emitting diode which is connected to and controlled by the astable multivibrator. One object of the invention is to provide a low cost clock which has good precision. Other objects and advantages will be apparent from the following Summary and Detailed Description of the preferred embodiments.
In accordance with the present invention, the device is provided with a mechanism that is active at least when the device is switched off, for periodically starting the micro-controller. When the micro-controller is on, the mechanism calibrates the frequency of the low accuracy oscillator with help of the high accuracy clock. Additionally, the device including a means for using the result of the calibration in order to display a corrected time.
It is possible to implement a low cost time display function, for instance in a car radio, using a low cost oscillator, as far as the clock of the micro-controller is based on a crystal. The accuracy of the time display is roughly the accuracy of the crystal, i.e. the influence of other devices is negligible.
These and other more detailed aspects of the invention will be apparent from the following description of an exemplary embodiment of the invention.